In certain lamps of the above type, it is important that the light-generating means be precisely located in a predetermined position within the envelope of the lamp. For example, in a metal-halide discharge lamp, light is generated by an arc developed between spaced electrode tips, and these tips must be precisely located with respect to each other and the surrounding envelope in order to achieve proper envelope or arc-tube temperature distribution and desired optical properties, life, and lumens output. The electrode tips are located by supporting them on leads which extend through openings in the envelope, and seals are formed between the envelope and the leads in order to support the leads on the envelope and to prevent any leakage in this region. The seals can be either of the pinch-seal type or the shrink-seal type.
One obstacle to achieving precise positioning of the electrode tips is the difficulty of making the seals without introducing such distortion of the sealing regions of the envelope that displaces the leads and electrode tips from the precise positions desired. We are concerned with providing a seal and support structure for the leads that lends itself to achieving precise positioning of the light-generating means, for example, the electrode tips in the case of a discharge lamp.
In addition to the need for precise positioning of the electrode tips, there is a need to hold the inner geometry of the light-transmitting envelope to close design tolerances in order to meet certain color separation, life, and quality requirements. The above-described difficulty of making the seals about the leads without introducing distortion of the sealing regions of the envelope is an obstacle to achieving the precise inner geometry desired for the envelope. We are concerned with providing seal and support structure for the leads that facilitates achieving the precise desired inner geometry of the envelope.
We are also concerned with providing a method of constructing the seal and support structure that enables us to achieve precise positioning of the light-generating means and precise control of the inner geometry of the envelope.
Our invention is also applicable to filament type lamps, e.g., the double-ended halogen lamp containing a tungsten filament and one or more halogens within the filament chamber, with the surface of the filament chamber having a coating or filter thereon which transmits visible light radiation but which reflects infrared radiation back to the filament. Such lamps require precise radial alignment of the filament along the optical axis of the filament chamber in order to achieve maximum conversion of the infrared radiation reflected by the coating back to the filament to visible light radiation which is transmitted by the coating. A lamp of this type is disclosed and claimed in U.S. Pat. No. 4,942,331--Bergman et al, assigned to the assignee of the present invention.